Process of electroplating rhenium and bath for this process

ABSTRACT

The invention relates to a bath for electrodepositing low-stress rhenium and its alloys of the perrhenate type and is characterized by the addition of ions which make up one or more of the following salts: magnesium sulfate, magnesium sulfamate, aluminum sulfate and aluminum sulfamate. The invention also relates to the process of electroplating from said bath.

United States Patent Meyer et al.

PROCESS OF ELECTROPLATING RHENIUM AND BATH FOR THIS PROCESS Inventors:

Donald Gardner Foulke, Passaic, N .J

Assignee: Sel-Rex Corporation, Nutley, NJ. Filed; Oct. 27, 1970 Appl. No.1 84,505

Related U.S. Application Data Continuation of Ser. No; 739,165, June 24, 1926, abandoned.

Foreign Application Priority Data July 3, 1967 Switzerland ..9470/67 us. 01 .Q ..204/43, 204/47 Int. Cl. ..cz3b 5/32,C23b 5/24 Andre Meyer, Geneva, Switzerland;v

[ 'June 6, 1972 Eldridge K. Camp, Plating, pp. 413- 416, May 1965.

Primary Examiner-G. L. Kaplan Attorney-Greene & Durr [57] ABSTRACT The invention relates to a bath for electrodepositing low-stress rhenium and its alloys of the perrhenate type and is characterized by the addition of ions which make up one or more of the following salts: magnesium sulfate, magnesium sulfamate, aluminum sulfate and aluminum sulfamate. The invention also relates to the process of electroplating from said bath.

10 Claims, No Drawings PROCESS OF ELECTROPLATING RHENIUM AND BATH FOR THIS PROCESS;

This application is a continuation of our U.S. Pat. application, Ser. No. 739,165, filed June 24, 1968 and now abandoned.

The present invention relates to a method for the electrodeposition of rhenium and to a bath for carrying out this method. v

Rhenium has manyinteresting properties. Its melting point is 3,] 80 C., its oxide is conductive and this metal is very hard and has a high density as well as good'reflectivity. These properties suggest its use under suitable high temperature conditions, for switching devices, as a protecting material against radiations and as a thennal shield. Rhenium has been plated for more than thirty years. However, the baths described in the literature give in general brittle'deposits, many cannot be used for heavy deposits and have efficiencies of under percent.

Many formulations for rhenium plating baths have been disclosed in the literature, all of which comprise the use of solutions containing perrhenate ions, ReO...

The object of the present invention is to provide a method and an electrolytic bath for the deposition of rhenium to heavy thicknesses at a good efficiency. A- second object of the invention is to permit the deposition of the rhenium in a lowstressed ductile condition.

The'method, according to the invention, is characterized by the fact that one uses a bath containing rhenium as the perrhenate ion and a salt selected from the group comprising magnesium sulfate, magnesium sulfamate, aluminum sulfate and aluminum sulfamate.

The bath according to the invention is characterized by the fact that it contains rhenium as the perrhenate ion and a-salt selected from the group comprising magnesium sulfate, magnesium sulfamate, aluminum sulfate and aluminum sulfamate.

It has been ascertained that the addition of magnesium sulfate and magnesium sulfamate to a bath containing the perrhenate ion adjusted to a pH value of less than 10 will produce thick, low-stressed deposits. Furthermore, the bath efiiciency, although still rather low, is of the order of 12 to 13 percent of the theoretical. When the pH is raised above 2, the efiiciency beings to fall ofi', so that a pH range of l to 2 is preferable. The pH .may. be reduced with sulfuric or a phosphoric acid. Hydrochloric acid is' not advisable because chlorides are detrimental. It is the magnesium ion which is effective but, obviously, magnesium oxide and carbonate can be added because they will be converted to sulfate or sulfamate in the solution.

The deposits are adherent, smooth and fully bright. Satisfactory deposits have been obtained on many basis metals. Where the high acidity attacks the basis metal, it should be plated first with nickel. In order to prevent contamination of the bath, the use of a gold strike, prior to the rhenium plating step, has been found helpful.

A typical bath, in grams per liter, is the following:

Potassium Pcrrhenate KReO.) 10 g/l Sulfuric acid (H 800 30 ml/l Magnesium sulfate (MgSO -7H O) 25 gll CONDITIONS.

pH: l.0

Current density: 10 Amp/dm Temperature: 60 (20 to 95C) EXAMPLE I vcodeposited with rhenium.

in that the efficiency is good and the evaporation of the solution is not excessive. 7

EXAMPLE 2 The substitution of 25 gll of magnesium sulfamate for the magnesium sulfate in the typical bath described above yielded deposits which appear to be even less stressed on the basis of a qualitative test, so it appears that the magnesium ion is the effective agent, but that the anion also has an effect. The deposits were bright and adherent to the nickel basis metal provided with a gold-strike. The amount of rhenium added as the perrhenate ion is not limited to 10 gll as' 'given in the example. This may be varied from 2 g/l to 50 g/l. For cost reasons, the concentration of rhenium is usually from 10 to l5 gll.

The amount of magnesium salt required is not critical in that it can be varied over a wide range. However, it appears that the lower limit at which the salt is effective is about 5 g/l and that quantities above 50 g/l do not produce any improvement. However, the scope of the invention is not limited to the higher value mentioned, because amounts of magnesium salt up to saturation can be used.

ltis possible to add metallic ions to the magnesium-containing perrhenate solution and to obtain alloys which, likewise, exhibit low stress. Nickel, cobalt, indium and gold have been EXAMPLE 3 Examples 1 and 2 indicate the simplest formulation, i.e., a solution containing the perrhenate ion and; magnesium sulfate with the pH lowered to l or 2 with sulfuric and sulfamic acids respectively.The amount of acid is conveniently 2 to 25 g/l,

but these data are not critical. It is sometimes helpful to add to the simple solutions conducting salts such as ammonium sulfate or sulfamate. A typical formula is as follows:

Potassium perrhenate l0 gll Sulfuric acid 10 gll Ammonium sulfate 25 gll Magnesium sulfate 25 g/l CONDITIONS: I pl-I: .2

- Cur-rent densityz, l2 Amp/dm Temperature: 65C

Deposits obtained from this bath were bright and hard and the current density efficiency was 10 percent.

It has been moreover discovered that a bath containing the perrhenate ion along with magnesium sulfate and/or sulfamate along with the perchlorate ion will produce thick, low-stressed deposits at a plating rate of almost 3 mg/Ampere-minute. These baths are more efiicient at a pH of 1 to 2 but are operav previously obtained. Since the bath is normally quite acid, it is advisable to preplate acid-soluble basis metals'with-nickel, the

nickel coating itself should be goldflashed .tominimize the contamination of the bath by nickel impurities. Of course, when plating rhenium-nickel alloys, this is not necessary.

EXAMPLE 5 A bath was prepared containing:

Rhenium (as potassium perrhenate) Deposits obtainedfrom the above bath at 60 C. and at Amp/dm were bright and ductile. The plating rate was 2.78 mg/Ampere-minute while the rate '-for the standard bath, containing neither the perchlorate nor the magnesium sulfate, is of the 1.2 mg/Ampere-minute. Adding the magnesium sulfate only, but notthe perchlorate as in Example 3, increased the rate of 1.5 mg/Ampere-minute. The addition of the perchlorate improved this rate by more than 80 percent,

bringing it tothe above mentioned figure of 2.78 mg/Ampereminute, the depositing having moreover a brighter ap I At 10 Amp/dr'n and60 C. bright deposits were obtained from this bath, at the rate of 2.47 mg/Ampere-minute.

EXAMPLE 7 To the bath described in Example 5 were added 20 g/l of nickel sulfate. The deposit was bright and rather ductile, differin'g in color from that of Example 5, indicating the formation of a rhenium-nickel alloy. The plating conditions were the same as for Example 5.

EXAMPLE 8 To the bath of Example 6 were added 10 g/l of cobalt sulfate and, as in this example, a bright alloy deposit was obtained.

The. features and principles underlying the invention described above in connection with specific exemplifications will suggest to those skilled in the art many other modifications thereof. It is accordingly desired that the appended claims shall not be limited to any specific feature or details thereof.

We claim: 1

1. An aqueous electroplating bath for the electrodeposition of low-stress deposits of rheniumand its alloys comprising from 2 to grams of rhenium as the perrhenate ion per liter of bath, and the ions from at least one salt selected from the group consisting magnesium sulfamate, aluminum sulfate, and aluminum sulfamate, the concentration of said salt ranging from about 5 grams per liter of bath up to its saturation concentration, said bath being maintained at a pH of less than 10.

2. The aqueous electroplating bath of claim 1 comprising in addition at least one conducting salt selected from the group consisting of alkali metal and ammonium salts of sulfuric, sulfamic and perchloric acids. 1

3. The aqueous electroplating bath of claim 1 comprising in addition free acid selected from the group consisting of perchloric, sulfuric and sulfamic acids. v v

4. The aqueous electroplating bath of claim 1 comprising, in addition to the perrhenate ions, ions of an electrodepositable metal, added as a soluble salt of the metal. 5. The aqueous electroplating bath of claim 1 wherein the bath is maintained at a pH of l to 2. 1

6. A method of electrodepositing rhenium and its alloys which comprises electrolyzing, at a current density of 2 to 30 amp/dm measured at the cathode, an aqueous bath comprising from 2 to 50 grams of rhenium as the perrhenate ion per liter of bath and at least one salt selected from the group consisting of magnesium sulfate, magnesium sulfamate, aluminum sulfate and aluminum sulfamate, the concentration of said salt ranging from about 5 grams per liter of bath up to its saturation concentration, said bath being maintained at a pH of less than 10.

7. The method of claim 6 wherein said bath contains at least one conducting salt selected from the group consisting of alkali metal and ammonium salts of sulfuric, sulfamic and perchloric acids.

8. The method of claim 6 whereinsaid bath contains in addition free acid selected from the group consisting of perchloric, sulfuric and sulfamic acids.

9. The method as claimed in claim 6 wherein said bath contains, in addition to the perrhenate ion, at least one ion of a metal which is codeposited with the rhenium.

10. The method of claim 6 wherein the bath is maintained at a pH of l to 2. 

2. The aqueous electroplating bath of claim 1 comprising in addition at least one conducting salt selected from the group consisting of alkali metal and ammonium salts of sulfuric, sulfamic and perchloric acids.
 3. The aqueous electroplating bath of claim 1 comprising in addition free acid selected from the group consisting of perchloric, sulfuric and sulfamic acids.
 4. The aqueous electroplating bath of claim 1 comprising, in addition to the perrhenate ions, ions of an electrodepositable metal, added as a soluble salt of the metal.
 5. The aqueous electroplating bath of claim 1 wherein the bath is maintained at a pH of 1 to
 2. 6. A method of electrodepositing rhenium and its alloys which comprises electrolyzing, at a current density of 2 to 30 amp/dm2 measured at the cathode, an aqueous bath comprising from 2 to 50 grams of rhenium as the perrhenate ion per liter of bath and at least one salt selected from the group consisting of magnesium sulfate, magnesium sulfamate, aluminum sulfate and aluminum sulfamate, the concentration of said salt ranging from about 5 grams per liter of bath up to its saturation concentration, said bath being maintained at a pH of less than
 10. 7. The method of claim 6 wherein said bath contains at least one conducting salt selected from the group consisting of alkali metal and ammonium salts of sulfuric, sulfamic and perchloric acids.
 8. The method of claim 6 wherein said bath contains in addition free acid selected from the group consisting of perchloric, sulfuric and sulfamic acids.
 9. The method as claimed in claim 6 wherein said bath contains, in addition to the perrhenate ion, at least one ion of a metal which is codeposited with the rhenium.
 10. The method of claim 6 wherein the bath is maintained at a pH of 1 to
 2. 